1. Field of the Invention
The invention relates to a sealing glass substrate for organic EL (electroluminescent) material and a method of manufacturing an organic EL display using the sealing glass substrate. More specifically, the invention relates to a sealing glass substrate for organic EL material, provided with an escape groove for adhesive in an outer periphery of an adhesion member.
2. Description of the Related Art
A conventional sealed organic EL display, a bottom emission type sealed organic EL display in particular, has a structure shown in FIGS. 1A, 1B and 1C. The organic EL display in the sectional view of FIG. 1A includes a laminate 12 having a transparent electrode, an organic EL layer, a reflection electrode formed on a glass substrate 11, and a lead out terminal 17a electrically connected to the reflection electrode of the laminate 12. An adhesive 13 is applied around the laminate 12 and adheres the laminate to a sealing glass substrate 14.
The organic EL layer, being very vulnerable to oxygen and moisture, easily loses its ability to emit light upon exposure to the atmosphere. Accordingly, an organic EL layer is usually sealed by a sealing glass substrate 14 having a moisture absorber 15 disposed opposing the laminate 12 in a chamber with extremely reduced oxygen and moisture. To prevent the organic EL layer and other laminated films from being touched, and to ensure that a space is provided for accommodating the moisture absorber, a recess may be created in the sealing substrate in the portion opposing the laminate of the organic EL layer and other films. The adhesive 13 can be of the type that hardens in response to application of ultraviolet light, for example. FIG. 1B is a plan view of this structure taken from the side of the glass substrate 11. An organic EL display area for light emission from the organic EL layer is formed in the location corresponding to the laminate 12. A sealing region is formed in the area corresponding to the adhesive 13. FIG. 1C is a plan view of this structure taken from the side of the sealing glass substrate 14 in which lead out terminals 17a and 17b are exposed. The lead out terminal 17a is electrically connected to the reflection electrode and the lead out terminal 17b is electrically connected to the transparent electrode.
Mass production of organic EL displays is generally carried out by forming multiple organic EL display areas on a glass substrate, sealing with a sealing glass substrate, and then cutting those substrates to form multiple organic EL displays. FIG. 2 shows a sealing substrate 21 and a substrate 25 for multiple organic EL displays. The substrate 25 includes multiple combinations of a laminate 26 containing a transparent electrode, an organic EL layer, and other layers (which forms an organic EL display area together with a reflection electrode) and a lead out terminal 27 electrically connected to the reflection electrode adjacent to the laminate 26. The sealing substrate 21 has recesses 22 at positions opposing the respective laminates 26. Adhesive is applied around each recess 22 by means of a dispenser or by screen printing, and the two substrates are laminated as shown in FIGS. 3A, 3B and 3C. FIG. 3A is a sectional view, FIG. 3B is a plan view taken from the side of the substrate 25, and FIG. 3C is a plan view taken from the side of the sealing substrate 21. In the laminating process, the adhesive (ultraviolet light-hardening resin) is pressed by exerting external pressure after the elements are combined, or the elements are combined under a reduced pressure and then atmospheric pressure is restored. After curing the adhesive by irradiating it with ultraviolet light, the sealing substrate 21 is cut along the line 32, and the substrate 25 is cut-along the line 31, to obtain the shape shown in FIG. 1A. The cutting is carried out primarily by a scribe method in which small nicks are formed on the glass surface using a diamond cutter or the like, and then cracks are developed by striking from the back side or exerting stress to cleave the glass.
The use of a material other than glass for the sealing substrate has been proposed. (See Japanese Unexamined Patent Application Publication No. 2001-189191 and Japanese Unexamined Patent Application Publication No. 2000-100562). In the structure shown in Japanese Unexamined Patent Application Publication No. 2001-189191, two grooves are formed at both sides of an adhesion application region of a sealing plate of stainless steel manufactured by drawing control, and expansion of the adhesive is restrained. The sealing plate in Japanese Unexamined Patent Application Publication No. 2001-189191 is, however, not planar and has a shape difficult to fabricate of glass. In addition, the adhesive is permitted to expand laterally beyond the grooves and the structure does not take into account the cutting after sealing.
Japanese Unexamined Patent Application Publication No. 2000-100562 discloses a structure that restrains invasion of adhesive into a space for accommodating a light emitting part, by disposing a groove on an adhesive application region in a sealing body of metal or the like. The sealing board disclosed in Japanese Unexamined Patent Application Publication No. 2000-100562 is, again, not planar, and difficult to fabricate with glass. The structure restrains invasion of adhesive into a space for accommodating a light emitting part by permitting outward expansion of the adhesive, and therefore does not consider cutting work after the sealing.
In the method of manufacturing the organic EL display of FIGS. 1A, 1B and 1C, from the combination of FIGS. 3A, 3B and 3C, the adhesive may run off from the predetermined location and extend laterally in the process of laminating the two substrates 21 and 25. If the runoff adhesive expands to the cutting position, the produced nick fails to cut the glass at the desired position (see FIG. 6A). Even if a nick is produced in an area the adhesive exists, the crack does not extend, or extends to a direction where the adhesive is absent, generating defects such as flaking, burrs, and cracking, as illustrated in FIGS. 9A, 9B and 9C, respectively.
Accordingly, the cutting position must be determined in the outside region from the extended adhesive with enough clearance. Or if some restriction is imposed on the cutting position, the adhesion width is narrowed or the adhesive is not pressed strongly, preventing the adhesive from expanding uncontrollably from the position at which it is applied.
Control of the degree of expansion of the width of the adhesive becomes difficult as the degree to which the substrates are of squeezed together increases and requires excessive space. As a result, a peripheral region of an EL display area called “a picture frame” expands, and the external dimension of the display enlarges, thus decreasing the number of displays that can be produced from one substrate and causing an increase of the cost. The narrowing of the width of adhesion and the decrease in the amount of squeeze, on the other hand, cause a decrease in sealing performance and leads to a corresponding degradation of the organic EL layer from oxygen or moisture.
Penetrating the glass substrate to form a recess generates distortion of several tens of microns in the height around the recess, making it is difficult to apply adhesive uniformly around it. If the application is nonuniform, then uniform pressing causes different degrees of expansion of the adhesive (adhesion width) from place to place. If a precise application of adhesive is desired on a distorted surface, a costly system, which measures the height of the surface to which the adhesive is to be applied and applies the adhesive strictly following the height, would be needed.